The invention relates to the manufacture of semiconductor devices and, more particularly, to a method for manufacturing a photomask used in a photolithography process.
During the manufacture of semiconductor devices, a photolithography process is performed to transcribe a circuit pattern on a wafer. The photolithography process uses a photomask having a mask pattern for the circuit pattern to be transcribed. As the design rule of semiconductor devices reduces, the photomask is manufactured to have a phase shift mask (PSM) structure including a mask pattern of a phase shift layer to improve resolution in an exposure process. A phase shift mask (PSM) improves pattern resolution in the exposure process by using an interference phenomenon due to a phase difference between light passing through a quartz mask substrate and light passing through the mask pattern of the phase shift layer. However, after the PSM is manufactured, it is occasionally necessary to modify or correct the line width of the mask pattern of the PSM.
FIGS. 1 and 2 are schematic diagrams for explaining a wafer exposure process using the phase shift mask (PSM).
Referring to FIG. 1, a phase shift mask (PSM) 20 including a transparent quartz mask substrate 21 and a mask pattern 23 of a phase shift layer disposed on the quartz mask substrate 21 is provided on the wafer to perform the exposure process. In this case, a wafer pattern having a desired line width may not be transcribed on the wafer and, as a result, a line width variation may occur in a certain portion of the wafer. In order to check whether the line width variation occurs, the line width of the wafer pattern (e.g., the photoresist pattern) formed on the wafer after the exposure process is measured to provide line width data, i.e., critical dimension (CD) data in a wafer map as shown in FIG. 2. By inspecting a wafer map 11 representing the line width a CD variation may be detected in a region of interest 12.
As for the region 12 where the CD variation is detected, it may be necessary to modify the line width of the mask pattern. 23 of the PSM 20. However, in case of an attenuated PSM, it is difficult to modify or correct the mask pattern by feeding back the line width data of the wafer pattern. Accordingly, in order to feed back the line width data onto the PSM, in substance it is necessary to manufacture a new PSM. Therefore, in order to reduce the time and cost required for the manufacture of the new PSM, it is necessary to develop a method for modifying the mask pattern of the PSM or for rectifying the line width variation of the wafer pattern on the PSM.